Method and system for detecting fault of serial coil type permanent magnet motor

ABSTRACT

A method and system for detecting a fault of a serial coil type permanent magnet motor includes driving the motor based on a predefined current reference value, detecting a phase current vector of the motor, and calculating a current compensation value for removing a negative sequence component of the motor based on the phase current vector. The current compensation value is provided to a negative sequence current controller for calculating a faulty phase and a degree of a fault of the motor using the output of the negative sequence current controller and a fault model to which induced magnetic flux variations in a specific slot of a specific faulty phase of the motor and other slots of the same phase as the specific phase are applied, and applying a current reference value to which the calculated faulty phase and degree of fault are applied.

FIELD

The present invention relates to a permanent magnet motor, and moreparticularly, to a method and system for detecting a fault of a serialcoil type permanent magnet motor, to detect a phase having a stator coilwinding inter-turn short circuit fault of the serial coil type permanentmagnet motor and the quantity of the fault on the basis of amathematical model.

BACKGROUND

In general, a motor includes a stator and a rotor. A small motor isconstructed in such a manner that a permanent magnet is used as astator, a coil is wound around a rotor and current is applied to thecoil to make the rotor function as a permanent magnet such that therotor rotates according to interaction between the stator and the rotor.In this structure, current is continuously supplied to the rotor evenwhile the rotor rotates by means of a brush.

With the recent development of semiconductors, a permanent magnet isused as a rotor, a coil is wound around a stator and power is suppliedto the stator. According to this structure, stators are sequentiallymagnetized to rotate the rotor magnetically corresponding to thestators. A motor of this type is called a permanent magnet synchronousmotor (PMSM). The PMSM can minimize power consumption and improve systemefficiency because a permanent magnet is used as a rotor to generatemagnetic flux without using an external power supply.

The structure of the PMSM can be classified according to arrangement ofa rotor and a stator. Particularly, a surface-mounted permanent magnetmotor (SPM) having a permanent magnet attached to the surface of a rotorgenerates sinusoidal back electromotive force through the permanentmagnet attached to a cylindrical shaft. The SPM generates a constanttorque all the time when sinusoidal current is applied to an armaturecoil.

In a conventional motor structure, a stator coil is covered by aninsulator such that inter-turn short circuit fault is not generatedbetween the stator coil and a neighboring coil. However, the insulatorcovering the coil may age over time or be damaged due to power or sparkinduced into the motor. Accordingly, the insulator may be stripped offto expose the coil and the exposed coil and a neighboring exposed coilare short-circuited. To solve this coil turn circuit, a conventionalfault detection method detects a motor fault only on the basis of a casein which power of a predetermined level is not output in initialoperation of a motor, and thus the cause of the motor fault cannot becorrectly detected and it is difficult to appropriately control themotor. Furthermore, since the conventional fault detection methodexperimentally applies a predetermined reference level, a considerabledeviation and error are generated. To reduce the deviation and error, alarge amount of experimental data needs to be acquired and thus effortsand expenses for the same are required.

SUMMARY

An object of the present invention is to provide a method and system fordetecting a fault of a serial coil type permanent magnet motor to easilyand accurately detect a fault due to inter-turn short circuit generatedbetween internal coils, caused by damage of an insulator of a statorcoil of the motor, and correctly detect a degree of the fault and aphase having the fault, facilitating analysis of the fault.

Another object of the present invention is to provide a method andsystem for detecting a fault of a serial coil type permanent magnetmotor to control motor operation on the basis of a stable motor controloperating point by estimating the quantity of fault current caused byinter-turn short circuit and appropriately limiting the quantity offault current.

One aspect of the present invention provides a system supportingdetection of a fault of a serial coil type permanent magnet motor. Thissystem includes a serial coil type motor, a current sensor configured tosense stator phase current of the motor, and a compensation currentcalculator configured to calculate a current compensation value for anegative sequence component generated in the motor on the basis of thesensed phase current. The system further includes a positive sequencecurrent controller configured to generate a control signal for aninverter control by using the current compensation value and also usinga current reference value provided from a control system, a negativesequence current controller configured to generate a signal for removingthe negative sequence component by using both the current compensationvalue and the current reference value, and then to provide the signal tothe positive sequence current controller, an inverter configured togenerate a motor operation signal according to the control signal, afault detector configured to detect a faulty phase and a degree of afault by applying the output of the negative sequence current controllerto a mathematically defined fault model, and the control systemconfigured to provide the current reference value to which the faultyphase and the degree of fault are applied. In this system, the faultmodel of the fault detector is a fault model to which a magnetic fluxvariation in a specific slot of a specific faulty phase of the motor andan induced magnetic flux variation in a slot of the same phase as thespecific phase are applied.

In this system, the compensation current calculator may be furtherconfigured to convert a 3-phase voltage into a 2-phase synchronousreference frame, and then to calculate the current compensation valuefor compensating for the negative sequence component.

Also, balanced currents of the motor for compensating for the negativesequence component may be

i_(a) = −I_(q)sin  θ + I_(d)cos  θ$i_{b} = {{{- I_{q}}{\sin \left( {\theta - \frac{2\pi}{3}} \right)}} + {I_{d}{\cos \left( {\theta - \frac{2\pi}{3}} \right)}}}$$i_{c} = {{{- I_{q}}{\sin \left( {\theta + \frac{2\pi}{3}} \right)}} + {I_{d}\cos \; {\left( {\theta + \frac{2\pi}{3}} \right).}}}$

And also, the motor may be a 3-phase motor and, and when a faultcorresponding to x (the ratio of a faultless coil to a faulty phase andfaulty pole pair) is generated in A-phase, a magnetic flux equation ofthe fault model may be

$\begin{bmatrix}v_{a} \\v_{b} \\v_{c} \\0\end{bmatrix} = {{R_{s}\begin{bmatrix}i_{a} \\i_{b} \\i_{c} \\i_{f}\end{bmatrix}} + {L_{s}{\frac{d}{dt}\begin{bmatrix}i_{a} \\i_{b} \\i_{c} \\i_{f}\end{bmatrix}}} + {\omega \; {\psi_{m}\begin{bmatrix}{{- \left( {1 - {\frac{2}{P}\left( {1 - x} \right)}} \right)}\sin \; \theta} \\{- {\sin \left( {\theta - \frac{2\pi}{3}} \right)}} \\{- {\sin \left( {\theta + \frac{2\pi}{3}} \right)}} \\{{- \left( {1 - x} \right)}\frac{2}{P}\sin \; \theta}\end{bmatrix}}}}$

wherein R_(s) and L_(s) are

$R_{s} = \begin{bmatrix}{R + {\left( {x - 1} \right)\frac{2}{P}R} + R_{f}} & 0 & 0 & {- R_{f}} \\0 & R & 0 & 0 \\0 & 0 & R & 0 \\{- R_{f}} & 0 & 0 & {{\left( {1 - x} \right)\frac{2}{P}R} + R_{f}}\end{bmatrix}$ $L_{s} = \begin{bmatrix}{{L_{m}\left( {1 + {\frac{2/P}{1 - \gamma}\left( {x^{2} - 1} \right)} + {\frac{\gamma \; {4/P}}{1 - \gamma}\left( {1 - x} \right)}} \right)} + {\left( {{\frac{2}{P}x^{2}} + 1 - \frac{2}{P}} \right)L_{l}}} & {\left( {{- \frac{1}{2}} + \frac{1 - x}{P}} \right)L_{m}} & {\left( {{- \frac{1}{2}} + \frac{1 - x}{P}} \right)L_{m}} & {{{- \left( {1 - x} \right)}\gamma \frac{2}{P}\frac{L_{m}}{1 - \gamma}} + {{x\left( {1 - x} \right)}\frac{2}{P}\frac{L_{m}}{1 - \gamma}}} \\{\left( {{- \frac{1}{2}} + \frac{1 - x}{P}} \right)L_{m}} & {L_{m} + L_{l}} & {{- \frac{1}{2}}L_{m}} & {{- \frac{1 - x}{P}}L_{m}} \\{\left( {{- \frac{1}{2}} + \frac{1 - x}{P}} \right)L_{m}} & {{- \frac{1}{2}}L_{m}} & {L_{m} + L_{l}} & {{- \frac{1 - x}{P}}L_{m}} \\{{{- \left( {1 - x} \right)}\gamma \; \frac{2}{P}\frac{L_{m}}{1 - \gamma}} + {{x\left( {1 - x} \right)}\frac{2}{P}\frac{L_{m}}{1 - \gamma}}} & {{- \frac{1 - x}{P}}L_{m}} & {{- \frac{1 - x}{P}}L_{m}} & {{\left( {1 - x} \right)^{2}\frac{2}{P}\frac{L_{m}}{1 - \gamma}} + {\frac{2}{P}\left( {1 - x} \right)^{2}L_{l}}}\end{bmatrix}$

wherein v_(a), v_(b), and V_(c), denote phase voltages of the motor, fdenotes a closed circuit generated caused by coil turn short, P is apole number, P/2 is a pole pair number, L_(m), and L_(l) respectivelydenote self inductance and leakage inductance of each phase when themotor is in a normal state, R is a phase resistance component, R_(f) isa contact resistance component generated due to inter-turn shortcircuit, x denotes the ratio of a faultless coil to a faulty pole, and γis a coupling factor of pole pairs in the same as a specific phase in aslot having the specific phase.

Additionally, fault current i_(f) due to turn short circuit may be

$\mspace{79mu} \begin{matrix}{i_{f} = {{\frac{{{R_{i\; 44}\left( {{\omega \; {I_{q}\left( {\text{?} - \text{?}} \right)}} - {\text{?}I_{d}}} \right)}\omega} - {\text{?}\left( {{\text{?}\omega \; I_{q}} + {\omega^{2}{\psi \left( {1 - x} \right)}\frac{2}{P}} + {\omega^{2}{I_{d}\left( {\text{?} - \text{?}} \right)}}} \right)\omega}}{\text{?} + \left( {\text{?}\omega} \right)^{2}}\cos \; \omega \; t} +}} \\{{\frac{{\text{?}\left( {{\text{?}\omega \; I_{q}} + {\omega^{2}{\psi_{m}\left( {1 - x} \right)}\frac{2}{P}} + {\omega^{2}{I_{d}\left( {\text{?} - \text{?}} \right)}}} \right)} + {\text{?}\left( {{\omega \; {I_{q}\left( {\text{?} - \text{?}} \right)}} - {\text{?}I_{d}}} \right)\omega^{2}}}{\text{?} + \left( {\text{?}\omega} \right)^{2}}\sin \; \omega \; {t.}}}\end{matrix}$ ?indicates text missing or illegible when filed

Furthermore, a synchronous reference frame value of a voltage valueobtained by filtering the output of the negative sequence currentcontroller may be as follows.

$\mspace{20mu} {\begin{bmatrix}\text{?} \\\text{?}\end{bmatrix} = {{{\frac{1}{3}\begin{bmatrix}{{I_{d}\left( {\text{?} + {2\; \text{?}}} \right)} + {\text{?}\; k_{1}} + {\omega \; {I_{q}\left( {{- \text{?}} + {2\; \text{?}} - {2\text{?}} + \text{?}} \right)}} + {\omega \; {k_{2}\left( {\text{?} - \text{?}} \right)}}} \\{{I_{q}\left( {\text{?} + {2\text{?}}} \right)} - {\text{?}k_{2}} - {\omega \; {I_{d}\left( {{- \text{?}} - {2\text{?}} + \text{?} + {2\; \text{?}}} \right)}} + {\omega \; {\psi_{m}\left( {3 - {\frac{2}{P}\left( {1 - x} \right)}} \right)}} + {\omega \; {k_{1}\left( {\text{?} - \text{?}} \right)}}}\end{bmatrix}}\mspace{20mu}\begin{bmatrix}\text{?} \\\text{?}\end{bmatrix}} = {\frac{1}{3}\begin{bmatrix}{{I_{d}\left( {\text{?} - \; \text{?}} \right)} + {\text{?}\; k_{1}} + {\omega \; {I_{q}\left( {{- \text{?}} + {2\; \text{?}} + \text{?} - {2L\text{?}}} \right)}} + {\omega \; {k_{2}\left( {\text{?} - \text{?}} \right)}}} \\{{- {I_{q}\left( {\text{?} + {2\text{?}}} \right)}} + {\text{?}k_{2}} + {\omega \; {\psi_{m}\left( {\frac{2}{P}\left( {1 - x} \right)} \right)}} + {\omega \; {I_{d}\left( {{- \text{?}} + {2\; \text{?}} + \text{?} - {2\; \text{?}}} \right)}} - {\omega \; {k_{2}\left( {\text{?} - \text{?}} \right)}}}\end{bmatrix}}}}$ ?indicates text missing or illegible when filed

Another aspect of the present invention provides a method for detectinga fault of a serial coil type permanent magnet motor. This methodincludes the steps of: driving the serial coil type permanent motorbased on a predefined current reference value; detecting a phase currentvector of the motor; calculating a current compensation value forremoving a negative sequence component of the motor based on the phasecurrent vector; providing the current compensation value to a negativesequence current controller and calculating a faulty phase and a degreeof a fault of the serial coil type permanent motor using the output ofthe negative sequence current controller and a fault model to whichinduced magnetic flux variations in a specific slot of a specific faultyphase of the serial coil type permanent motor and other slots of thesame phase as the specific phase are applied; and applying a currentreference value to which the calculated faulty phase and degree of faultare applied.

In this method, the step of applying the current reference value mayinclude adjusting the velocity and phase current of the motor based onthe faulty phase and degree of fault to suppress generation ofovercurrent.

According to the present invention, the method and system for detectinga fault of a serial coil type permanent magnet motor can easily detect amotor fault simply on the basis of only the form and parameter of themotor using a model instead of a test, easily detecting faults ofvarious motors.

Furthermore, the present invention can estimate motor fault current tooperate the motor without exacerbating the motor fault.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram illustrating the structure of a serial coiltype permanent magnet motor to which a fault model according to anembodiment of the present invention is applied.

FIG. 2 is a circuit diagram illustrating the permanent magnet motorshown in FIG. 1.

FIG. 3 illustrates a motor in the permanent magnet motor structure.

FIG. 4 shows an equivalent model for operation analysis of a motorhaving a fault.

FIG. 5 is a flowchart illustrating a method for detecting a fault of aserial coil type permanent magnet motor to which a fault model accordingto an embodiment of the present invention is applied.

FIGS. 6 and 7 are graphs for explaining accuracy of the fault modelaccording to the embodiment of the present invention.

DETAILED DESCRIPTION

In describing embodiments of the present invention, detaileddescriptions of constructions or processes known in the art may beomitted to avoid obscuring appreciation of the invention by persons ofordinary skill in the art to which the present invention pertains.

Accordingly, the meanings of specific terms or words used in thespecification and claims should not be limited to the literal orcommonly employed sense, but should be construed or may be different inaccordance with the intention of a user or an operator and customaryusages. Therefore, the definition of the specific terms or words shouldbe based on the contents of the specification. It should be understood,however, that there is no intent to limit the invention to theparticular forms disclosed, but on the contrary, the invention coversall modifications, equivalents, and alternatives falling within thespirit and scope of the invention as defined by the claims.

FIG. 1 is a block diagram illustrating the configuration of a permanentmagnet motor according to an embodiment of the present invention andFIG. 2 illustrates the configuration of the permanent magnet motor inmore detail. FIG. 3 shows the appearance of a motor in the permanentmagnet motor according to the present invention and FIG. 4 shows anequivalent model of a serial coil type motor according to the presentinvention.

Referring to FIGS. 1 to 4, a permanent magnet motor 10 according to thepresent invention may include a serial coil type motor 100, an inverter400, a current sensor 500, a positive sequence current controller 200, anegative sequence current controller 300, a compensation currentcalculator 600 and a fault detector 700. The permanent magnet motor 10according to the present invention may further include a control systemcapable of providing a current reference value using a degree of faultdetected by the fault detector 700.

The permanent magnet motor 10 having the above-mentioned configurationaccording to the present invention can detect power generated when theserial coil type motor 100 is driven and construct a mathematical modelrelating to the serial coil type motor 100 on the basis of the detectedpower. In this process, the permanent magnet motor 10 can confirmwhether a fault, for example, inter-turn short circuit is generated in astator of the serial coil type motor 100 using a pre-designed faultmodel. Particularly, the permanent magnet motor 10 according to thepresent invention can mathematically detect the form of a fault using afault model derived from a model of the serial coil type motor 100 anddetect not only a fault of the serial coil type motor 100 but also adegree of the fault and a phase having the fault.

The serial coil type motor 100 operates according to a control signalprovided by the inverter 400. The serial coil type motor 100 may includea stator 110 and a rotor 120, as shown in FIG. 3.

The rotor 120 can be located at the center of the stator 110 at apredetermined distance from the stator 110 such that the rotor 120 canrotate in a predetermined direction facing the stator 110. The rotor 120may include a shaft located at the center thereof, a rotor coresurrounding the shaft and having a predetermined width, protrusionsextended to the rotor core from the outer wall of the rotor core, andpermanent magnets having a first polarity, which are attached to theouter wall of the rotor core.

The stator 110 has a hollow cylindrical shape having a predeterminedthickness and includes a plurality of slots arranged at a predeterminedinterval. The stator 110 may have a cylindrical form such that it formsthe perimeter of the motor and the inside of the cylinder may correspondto a space in which the rotor 120 can be located. The stator 110 may beformed of a material capable of generating a magnetic circuit, such asiron. The stator 110 includes the plurality of slots each of which iswound by a coil by a predetermined number of winding turns. The stator110 may be arranged at a predetermined distance from the permanentmagnets having the first polarity, which are included in the rotor 120.External current may be sequentially supplied to the coils winding theslots of the stator 110. Accordingly, the slots of the stator 110sequentially function as electromagnets and the rotor 120 located insidethe stator 110 is rotated by the slots of the stator 110, which functionas electromagnets. Particularly, the first polarity permanent magnetscan rotate in a predetermined direction by forming a specific magneticcircuit with the slots of the stator 110.

As described above, the coils included in the stator 110 wind around theslots of a stator core. The outside of each coil is covered with aninsulator such that inter-turn short circuit is not generated betweenneighboring coils. However, the insulating property of the insulator isdeteriorated according to high voltage and heat with time, generatinginter-turn short circuit between neighboring coils. Inter-turn shortcircuit degrades the performance of the serial coil type motor 100, theturn-short coils form a circuit, and high current is induced accordingto magnetic flux of the magnets and the stator 110. The generated highcurrent causes copper loss to promote generation of heat and severedamage to the insulator of a near coil, destroying the serial coil typemotor 100 or resulting in fire. The permanent magnet motor 10 accordingto the present invention can mathematically model electrical variationin a coil due to inter-turn short circuit and can easily detect a phaseof the serial coil type motor 100, which has a fault, and a degree ofthe fault on the basis of the mathematical model.

The serial coil type motor 100 is designed such that it has3-phase-balanced impedance and counter electromotive force. In case ofturn short, impedance and counter electromotive force decrease only in aphase having inter-turn short circuit and a turn-short coil forms anindependent circuit. If the serial coil type motor 100 is driven whenthis kind of fault is generated, current or voltage is unbalanced tocause a negative sequence distinguished from normal 3 phases. Thenegative sequence has a rotational rate opposite to that of a positivesequence. If the positive sequence generates a rotating field in therotating direction of the serial coil type motor 100, the negativesequence forms a rotating field in the opposite direction. Accordingly,the rotating field of the negative sequence is regarded as disturbancetwice the rotating velocity of the positive sequence from the viewpointof the positive sequence. The negative sequence is a component in which3 phase of a, b and c are formed in the order or a, c and b,distinguished from the positive sequence in which the 3 phases areformed in the order of a, b and c. Phases b and c are mathematicallydifferent from each other. The positive sequence and negative sequencecan be represented by Equations 1 and 2.

$\begin{matrix}{{f_{ap} = {A_{p}{\cos ({wt})}}}{f_{bp} = {A_{p}{\cos\left( {{wt} - \frac{2\pi}{3}} \right)}}}{f_{cp} = {A_{p}{\cos\left( {{wt} + \frac{2\pi}{3}} \right)}}}} & \left\lbrack {{Equation}\mspace{14mu} 1} \right\rbrack \\{{f_{an} = {A_{p}{\cos ({wt})}}}{f_{bn} = {A_{p}{\cos\left( {{wt} + \frac{2\pi}{3}} \right)}}}{f_{cn} = {A_{p}{\cos\left( {{wt} - \frac{2\pi}{3}} \right)}}}} & \left\lbrack {{Equation}\mspace{14mu} 2} \right\rbrack\end{matrix}$

Here, f_(ap), f_(bp) and f_(cp) mathematically represent the 3-phasepositive sequence and f_(an), f_(bn), and f_(cn), mathematicallyrepresent the 3-phase negative sequence. As represented by theequations, the phases of the positive sequence and the negative sequenceare reverse to each other. The negative sequence is generated at phasecurrent or voltage of the motor although generation of the negativesequence depends on a control method.

The present invention can derive a mathematical model to a synchronousreference frame from abc coordinates of the motor and detect thequantity of a fault and a phase having the fault on the basis of themathematical model.

$\begin{matrix}{\begin{bmatrix}v_{a} \\v_{b} \\v_{c} \\0\end{bmatrix} = {{R_{s}\begin{bmatrix}i_{a} \\i_{b} \\i_{c} \\i_{f}\end{bmatrix}} + {L_{s}{\frac{d}{dt}\begin{bmatrix}i_{a} \\i_{b} \\i_{c} \\i_{f}\end{bmatrix}}} + {\omega \; {\psi_{m}\begin{bmatrix}{{- \left( {1 - {\frac{2}{P}\left( {1 - x} \right)}} \right)}\sin \; \theta} \\{- {\sin \left( {\theta - \frac{2\pi}{3}} \right)}} \\{- {\sin \left( {\theta + \frac{2\pi}{3}} \right)}} \\{{- \left( {1 - x} \right)}\frac{2}{P}\sin \; \theta}\end{bmatrix}}}}} & \left\lbrack {{Equation}\mspace{14mu} 3} \right\rbrack\end{matrix}$

Equation 3 is a magnetic flux equation of the motor in the abccoordinates on the assumption that a fault corresponding to x (the ratioof a good coil to a faulty phase and a faulty pole pair) is generated inA-phase. The model of the serial coil type motor 100 is based onconcentrated winding having 3N slot in case of 2N pole. R_(p) and L_(p)in Equation 3 can be represented by Equation 4.

$\begin{matrix}{{R_{s} = \begin{bmatrix}{R + {\left( {x - 1} \right)\frac{2}{P}R} + R_{f}} & 0 & 0 & {- R_{f}} \\0 & R & 0 & 0 \\0 & 0 & R & 0 \\{- R_{f}} & 0 & 0 & {{\left( {1 - x} \right)\frac{2}{P}R} + R_{f}}\end{bmatrix}}{L_{s} = {\quad\begin{bmatrix}{{L_{m}\left( {1 + {\frac{2/P}{1 - \gamma}\left( {x^{2} - 1} \right)} + {\frac{\gamma \; {4/P}}{1 - \gamma}\left( {1 - x} \right)}} \right)} + {\left( {{\frac{2}{P}x^{2}} + 1 - \frac{2}{P}} \right)L_{l}}} & {\left( {{- \frac{1}{2}} + \frac{1 - x}{P}} \right)L_{m}} & {\left( {{- \frac{1}{2}} + \frac{1 - x}{P}} \right)L_{m}} & {{{- \left( {1 - x} \right)}\gamma \frac{2}{P}\frac{L_{m}}{1 - \gamma}} + {{x\left( {1 - x} \right)}\frac{2}{P}\frac{L_{m}}{1 - \gamma}}} \\{\left( {{- \frac{1}{2}} + \frac{1 - x}{P}} \right)L_{m}} & {L_{m} + L_{l}} & {{- \frac{1}{2}}L_{m}} & {{- \frac{1 - x}{P}}L_{m}} \\{\left( {{- \frac{1}{2}} + \frac{1 - x}{P}} \right)L_{m}} & {{- \frac{1}{2}}L_{m}} & {L_{m} + L_{l}} & {{- \frac{1 - x}{P}}L_{m}} \\{{{- \left( {1 - x} \right)}\gamma \; \frac{2}{P}\frac{L_{m}}{1 - \gamma}} + {{x\left( {1 - x} \right)}\frac{2}{P}\frac{L_{m}}{1 - \gamma}}} & {{- \frac{1 - x}{P}}L_{m}} & {{- \frac{1 - x}{P}}L_{m}} & {{\left( {1 - x} \right)^{2}\frac{2}{P}\frac{L_{m}}{1 - \gamma}} + {\frac{2}{P}\left( {1 - x} \right)^{2}L_{l}}}\end{bmatrix}}}} & \left\lbrack {{Equation}\mspace{14mu} 4} \right\rbrack\end{matrix}$

In Equation 3, v_(a), v_(b), and V_(c) denote phase voltages of themotor and f denotes a closed circuit generated caused by coil turnshort. P is a pole number and P/2 is a pole pair number. In addition, xdenotes the ratio of a faultless coil to a faulty pole, L_(m), and L_(l)respectively denote self inductance and leakage inductance of each phasewhen the motor is in a normal state, and R is a phase resistancecomponent.

R_(f) is a contact resistance component generated due to inter-turnshort circuit and γ is a coupling factor of pole pairs in the same as aspecific phase in a slot having the specific phase. γ can improveaccuracy of a corresponding model when inter-turn short circuit isgenerated although γ is not applied to the balanced normal serial coiltype motor 100. That is, when the serial coil type motor 100 includesmultiple poles and magnetic flux generated in a coil slot of one phaseis varied, the flux variation affects magnetic flux generated in adistant coil slot in the same phase. For example, when magnetic fluxgenerated in a coil slot of one phase decreases, the quantity ofmagnetic flux transmitted to a distant coil slot having the same phaseis reduced. Accordingly, it is difficult to represent various states ofthe multi-pole serial coil type motor 100 using a simple equivalentmodel. While there is no need to consider deviation in the flux quantityin a balanced normal state, when an independent circuit loop isgenerated due to turn short, the independent circuit loop is coupledwith a coil of the same phase in a normal state and thus affected by thecoil. Accordingly, the present invention corrects the deviation using γ.That is, the fault detector 700 according to the present inventionapplies flux reduction generated due to turn short of a coil of aspecific phase in the motor having multiple phases and multiple poles tocalculation of inductance.

When the values of i_(a), i_(b) and i_(c) in Equation 3 are set usingthe compensation current calculator 600 such that negative sequencecurrent is not present and applied to the negative sequence currentcontroller 300, balance currents represented by Equation 6 can beapplied to the positive sequence current controller 200 and a signaloutput from the positive sequence current controller 20 can be appliedto the inverter 400.

$\begin{matrix}{{i_{a} = {{{- I_{q}}\sin \; \theta} + {I_{d}\cos \; \theta}}}{i_{b} = {{{- I_{q}}{\sin \left( {\theta - \frac{2\pi}{3}} \right)}} + {I_{d}{\cos \left( {\theta - \frac{2\pi}{3}} \right)}}}}{i_{c} = {{{- I_{q}}{\sin \left( {\theta + \frac{2\pi}{3}} \right)}} + {I_{d}\cos \; {\left( {\theta + \frac{2\pi}{3}} \right).}}}}} & \left\lbrack {{Equation}\mspace{14mu} 5} \right\rbrack\end{matrix}$

When the currents of Equation 5 are applied to Equation 3 to convert thecurrents and current i_(f) flowing through a separate independentcircuit according to turn short into the synchronous reference frame,Equation 6 can be obtained.

$\begin{matrix}{\mspace{79mu} {{{\begin{matrix}{i_{f} = {{\frac{{{R_{i\; 44}\left( {{\omega \; {I_{q}\left( {\text{?} - \text{?}} \right)}} - {\text{?}I_{d}}} \right)}\omega} - {\text{?}\left( {{\text{?}\omega \; I_{q}} + {\omega^{2}{\psi \left( {1 - x} \right)}\frac{2}{P}} + {\omega^{2}{I_{d}\left( {\text{?} - \text{?}} \right)}}} \right)\omega}}{\text{?} + \left( {\text{?}\omega} \right)^{2}}\cos \; \omega \; t} +}} \\{{\frac{{\text{?}\left( {{\text{?}\omega \; I_{q}} + {\omega^{2}{\psi_{m}\left( {1 - x} \right)}\frac{2}{P}} + {\omega^{2}{I_{d}\left( {\text{?} - \text{?}} \right)}}} \right)} + {\text{?}\left( {{\omega \; {I_{q}\left( {\text{?} - \text{?}} \right)}} - {\text{?}I_{d}}} \right)\omega^{2}}}{\text{?} + \left( {\text{?}\omega} \right)^{2}}\sin \; \omega \; {t.}}}\end{matrix}\mspace{20mu}\begin{bmatrix}\text{?} \\\text{?}\end{bmatrix}} = {{{\frac{1}{3}\begin{bmatrix}{{I_{d}\left( {\text{?} + {2\; \text{?}}} \right)} + {\text{?}\; k_{1}} + {\omega \; {I_{q}\left( {{- \text{?}} + {2\; \text{?}} - {2\text{?}} + \text{?}} \right)}} + {\omega \; {k_{2}\left( {\text{?} - \text{?}} \right)}}} \\{{I_{q}\left( {\text{?} + {2\text{?}}} \right)} - {\text{?}k_{2}} - {\omega \; {I_{d}\left( {{- \text{?}} - {2\text{?}} + \text{?} + {2\; \text{?}}} \right)}} + {\omega \; {\psi_{m}\left( {3 - {\frac{2}{P}\left( {1 - x} \right)}} \right)}} + {\omega \; {k_{1}\left( {\text{?} - \text{?}} \right)}}}\end{bmatrix}}\mspace{20mu}\begin{bmatrix}\text{?} \\\text{?}\end{bmatrix}} = {\frac{1}{3}\begin{bmatrix}{{I_{d}\left( {\text{?} - \; \text{?}} \right)} + {\text{?}\; k_{1}} + {\omega \; {I_{q}\left( {{- \text{?}} + {2\; \text{?}} + \text{?} - {2L\text{?}}} \right)}} + {\omega \; {k_{2}\left( {\text{?} - \text{?}} \right)}}} \\{{- {I_{q}\left( {\text{?} + {2\text{?}}} \right)}} + {\text{?}k_{2}} + {\omega \; {\psi_{m}\left( {\frac{2}{P}\left( {1 - x} \right)} \right)}} + {\omega \; {I_{d}\left( {{- \text{?}} + {2\; \text{?}} + \text{?} - {2\; \text{?}}} \right)}} - {\omega \; {k_{2}\left( {\text{?} - \text{?}} \right)}}}\end{bmatrix}}}}{\text{?}\text{indicates text missing or illegible when filed}}}} & \left\lbrack {{Equation}\mspace{14mu} 6} \right\rbrack\end{matrix}$

In application of the above equations, x becomes 1 when the serial coiltype motor 100 has no fault. Current components of the serial coil typemotor 100 can be controlled to be DC in a positive sequence synchronousreference frame of the serial coil type motor 100 having no fault. Whena fault is generated in the serial coil type motor 100, a negativesequence is generated as represented by the equation, a currentcompensation value for the negative sequence is calculated by thecompensation current calculator 600 and applied to the negative sequencecurrent controller 300, and then an output value of the negativesequence current controller 300 is applied to an output value of thepositive sequence current controller 200. Particularly, the faultdetector 700 filters the output signal of the negative sequence currentcontroller 300 to which the current compensation value calculated by thecompensation current calculator 600 has been applied and applies thefiltered signal to the above equations so as to detect the position of afaulty phase, that is, x. Upon detection of the faulty phase and x, itis possible to detect an operating point at which dielectric breakdowndoes not occur due to overcurrent in the serial coil type motor 100 bycontrolling a velocity and phase current which can limit i_(f). Toachieve this, the fault detector 700 can provide information about afault value to a control system.

The inverter 400 is configured to provide a predetermined voltage, e.g.3-phase voltage to the motor 100. The inverter 400 receives 3-phasecurrent generated and provided by a current controller, generates acontrol signal corresponding to the 3-phase current to produce aninverter voltage and supplies the inverter voltage to the serial coiltype motor 100. Particularly, the inverter 400 can generate a controlsignal for compensating for a fault of a specific phase due to turnshort of the serial coil type motor 100 and provide the control signalto the serial coil type motor 100. Here, signals supplied to theinverter 400 may include a signal corresponding to a current referencevalue to which a faulty phase and a degree of fault, detected by thefault detector 700, have been applied and a current compensation valuedetermined to remove a negative sequence component.

The positive sequence current controller 200 is configured to generate asignal corresponding to a current reference value pre-defined to drivethe serial coil type motor 100 and provide the generated signal to theinverter 400. Specifically, the positive sequence current controller 200receives a fault compensation value for compensating for a fault causedby inter-turn short circuit of the serial coil type motor 100 from thecompensation current calculator 600 and applies the fault compensationvalue to the current reference value to generate a signal to be providedto the inverter 400. Particularly, the positive sequence currentcontroller 200 can receive the current reference value to which thefaulty phase and the degree of fault detected by the fault detector 700from the control system, apply the output value of the negative sequencecurrent controller 300 to the current reference value, and then providethe current reference value to the inverter 400. Accordingly, thepositive sequence current controller 200 according to the presentinvention can generate and provide a signal corresponding to a currentvalue that minimizes error caused by inter-turn short circuit even whenthe inter-turn short circuit is generated in the serial coil type motor100.

The negative sequence current controller 300 is configured to generatean output value to which a current compensation value calculated tominimize a negative sequence component generated during operation of theserial coil type motor 100 and an output value to which the currentreference value provided by the control system have been applied. Thevalue generated by the negative sequence current controller 300 can beprovided to the fault detector 700 and the positive sequence currentcontroller 200.

The current sensor 500 is configured to sense a signal supplied from theinverter 400 to the serial coil type motor 100 or a signal according tooperation of the serial coil type motor 100. The current sensor 500senses a 3-phase current signal or a 3-phase voltage signal provided tothe serial coil type motor 100 and provides the sensed signal to thecompensation current calculator 600. Particularly, the current sensor500 can sense a 3-phase current signal according to operation of theserial coil type motor 100 and provide the sensed 3-phase current signalto the compensation current calculator 600. Here, the sensed 3-phasecurrent signal corresponds to current sensing values at positions atwhich 3 phases can be discriminated and can be represented as a currentvector.

The compensation current calculator 600 is configured to calculate acurrent compensation value according to the current reference valueusing current vector values sensed by the current sensor 500 and providethe current reference value to the positive sequence current controller200 and the negative sequence current controller 300. The compensationcurrent calculator 600 can convert the 3-phase current signal sensed bythe current sensor 500 into a 2-phase d-q synchronous reference frame,perform filtering and calculate a 2-phase d-q synchronous referenceframe signal using a rotating phasor for application of polarcoordinates. The current compensation value calculated by thecompensation current calculator 600 is a value for removing the negativesequence component.

The fault detector 700 filters the signal supplied from the negativesequence current controller 300 to the positive sequence currentcontroller 200 into a DC component and applies the DC component to acorresponding equation. The fault detector 700 is configured to providea d-q synchronous reference frame voltage according to generation offault. The fault detector 700 mathematically considers inductance in aphase having a fault and, particularly, can calculate the inductance inconsideration of the influence of magnetic flux generated in a specificslot of a specific phase on a different slot of the same phase. That is,the fault detector 700 can calculate a value controlling negativesequence current generated in the serial coil type motor 100 moreaccurately by considering flux variation in a different slot of the samephase when L_(p) in Equation 4 is applied, and thus the fault detector700 can support operation of the serial coil type motor 100 such thatthe influence of inter-turn short circuit of the serial coil type motor100 is minimized. Accordingly, the fault detector 700 can confirm x inthe serial coil type motor 100 having a fault on the basis of the outputof the negative sequence current controller 300 and the fault modelconfigured using the above equations.

FIG. 5 is a flowchart illustrating a method for detecting a fault of aserial coil type permanent magnet motor according to an embodiment ofthe present invention.

Referring to FIG. 5, the positive sequence current controller 200generates a control signal of the inverter 400 according to apre-defined current reference value and provides the generated controlsignal to the inverter 400 in step S101.

The inverter 400 generates a control signal for driving the serial coiltype motor 100 on the basis of the output of the positive sequencecurrent controller 200 and provides the generated control signal to theserial coil type motor 100 to drive the serial coil type motor 100 instep S103.

The current sensor 500 detects current vectors according to operation ofthe serial coil type motor 100 and provides the detected current vectorsto the compensation current calculator 600 in step S105. Then, thecompensation current calculator 600 calculates a current compensationvalue for removing a negative sequence component on the basis of thecurrent vectors in step S107.

Upon calculation of the current compensation value by the compensationcurrent detector 600, the current compensation value is provided to thenegative sequence current controller 300 and the positive sequencecurrent controller 200 in step S109. Here, the fault detector 700detects a faulty phase and a degree of fault by applying a fault valueof a negative sequence component, output from the negative sequencecurrent controller 300, to a magnetic flux equation in step S111. Toachieve this, the fault detector 700 can configure a fault modelconsidering a specific phase in which inter-turn short circuit isgenerated and a degree of fault in the specific phase using a magneticflux equation obtained by applying a negative sequence current componentto a positive sequence current component. Particularly, the faultdetector 700 applies an induced flux variation γ capable of using notonly a flux variation generated in a specific slot of a specific phasehaving a fault but also a flux variation generated in a different slotof the same phase, induced according to the flux variation of the samephase, to inductance of the magnetic flux equation. Accordingly, thefault detector 700 according to the present invention can accuratelyapply an actual negative sequence component generated in the serial coiltype motor 100 to the fault model to control a motor velocity and phasecurrent optimized to the fault model. Fault values detected by the faultdetector 700 are provided to the control system that provides a currentreference value. The control system can generate the current referencevalue to which the fault values have been applied and provide thecurrent reference value to the positive sequence current controller 200and the negative sequence current controller 300.

FIGS. 6 and 7 are graphs showing model accuracy according to applicationof the fault model according to an embodiment of the present invention.FIG. 6 shows FEM simulation based accuracy and FIG. 7 shows i_(f)current accuracy.

FIG. 6 shows values measured on the basis of a 6-pole 9-slot serial coiltype motor (rated 18 Vrms) and x=0.6666 (in case of coil turn short of300% in one slot) to check model accuracy through FEM analysis. Thegraph of FIG. 6 shows a negative sequence voltage output. In FIG. 6,x-axis shows Vde- and y-axis shows Vqe-. It can be known from FIGS. 6and 7 that the negative sequence voltage output and current i_(f) verysimilar to actual values are detected. Particularly, the fault modelaccording to the present invention can be easily applied to varioustypes of motors because the fault model is mathematically calculated.

As described above, the method for detecting a fault of a serial coiltype permanent magnet motor and the system supporting the same accordingto embodiments of the present invention detect a fault caused byinter-turn short circuit of the serial coil type motor 100 using themathematically configured fault model and, when a fault is generated,accurately detects a faulty phase and a degree of fault in considerationof a flux variation in a slot of a phase having turn short and fluxvariations in other slots of the same phase. Accordingly, the presentinvention can calculate an operating point at which the serial coil typemotor 100 is not additionally damaged and drive the serial coil typemotor 100 by applying a correct current reference value and a negativesequence current compensation value suitable to the faulty phase and thedegree of fault.

The detailed description of the preferred embodiments of the presentinvention has been given to enable those skilled in the art to implementand practice the invention. Although the invention has been describedwith reference to the preferred embodiments, those skilled in the artwill appreciate that various modifications and variations can be made inthe present invention without departing from the spirit or scope of theinvention described in the appended claims.

What is claimed is:
 1. A system supporting detection of a fault of a serial coil type permanent magnet motor, the system comprising: a serial coil type motor; a current sensor configured to sense stator phase current of the motor; a compensation current calculator configured to calculate a current compensation value for a negative sequence component generated in the motor on the basis of the sensed phase current; a positive sequence current controller configured to generate a control signal for an inverter control by using the current compensation value and also using a current reference value provided from a control system; a negative sequence current controller configured to generate a signal for removing the negative sequence component by using both the current compensation value and the current reference value, and then to provide the signal to the positive sequence current controller; an inverter configured to generate a motor operation signal according to the control signal; a fault detector configured to detect a faulty phase and a degree of a fault by applying the output of the negative sequence current controller to a mathematically defined fault model; and the control system configured to provide the current reference value to which the faulty phase and the degree of fault are applied, wherein the fault model of the fault detector is a fault model to which a magnetic flux variation in a specific slot of a specific faulty phase of the motor and an induced magnetic flux variation in a slot of the same phase as the specific phase are applied.
 2. The system of claim 1, wherein the compensation current calculator is further configured to convert a 3-phase voltage into a 2-phase synchronous reference frame, and then to calculate the current compensation value for compensating for the negative sequence component.
 3. The system of claim 2, wherein balanced currents of the motor for compensating for the negative sequence component are i_(a) = −I_(q)sin  θ + I_(d)cos  θ $i_{b} = {{{- I_{q}}{\sin \left( {\theta - \frac{2\pi}{3}} \right)}} + {I_{d}{\cos \left( {\theta - \frac{2\pi}{3}} \right)}}}$ $i_{c} = {{{- I_{q}}{\sin \left( {\theta + \frac{2\pi}{3}} \right)}} + {I_{d}\cos \; {\left( {\theta + \frac{2\pi}{3}} \right).}}}$
 4. The system of claim 3, wherein the motor is a 3-phase motor and, and when a fault corresponding to x (the ratio of a faultless coil to a faulty phase and faulty pole pair) is generated in A-phase, a magnetic flux equation of the fault model is $\begin{bmatrix} v_{a} \\ v_{b} \\ v_{c} \\ 0 \end{bmatrix} = {{R_{s}\begin{bmatrix} i_{a} \\ i_{b} \\ i_{c} \\ i_{f} \end{bmatrix}} + {L_{s}{\frac{d}{dt}\begin{bmatrix} i_{a} \\ i_{b} \\ i_{c} \\ i_{f} \end{bmatrix}}} + {\omega \; {\psi_{m}\begin{bmatrix} {{- \left( {1 - {\frac{2}{P}\left( {1 - x} \right)}} \right)}\sin \; \theta} \\ {- {\sin \left( {\theta - \frac{2\pi}{3}} \right)}} \\ {- {\sin \left( {\theta + \frac{2\pi}{3}} \right)}} \\ {{- \left( {1 - x} \right)}\frac{2}{P}\sin \; \theta} \end{bmatrix}}}}$ wherein R_(s) and L_(s) are $R_{s} = \begin{bmatrix} {R + {\left( {x - 1} \right)\frac{2}{P}R} + R_{f}} & 0 & 0 & {- R_{f}} \\ 0 & R & 0 & 0 \\ 0 & 0 & R & 0 \\ {- R_{f}} & 0 & 0 & {{\left( {1 - x} \right)\frac{2}{P}R} + R_{f}} \end{bmatrix}$ $L_{s} = \begin{bmatrix} {{L_{m}\left( {1 + {\frac{2/P}{1 - \gamma}\left( {x^{2} - 1} \right)} + {\frac{\gamma \; {4/P}}{1 - \gamma}\left( {1 - x} \right)}} \right)} + {\left( {{\frac{2}{P}x^{2}} + 1 - \frac{2}{P}} \right)L_{l}}} & {\left( {{- \frac{1}{2}} + \frac{1 - x}{P}} \right)L_{m}} & {\left( {{- \frac{1}{2}} + \frac{1 - x}{P}} \right)L_{m}} & {{{- \left( {1 - x} \right)}\gamma \frac{2}{P}\frac{L_{m}}{1 - \gamma}} + {{x\left( {1 - x} \right)}\frac{2}{P}\frac{L_{m}}{1 - \gamma}}} \\ {\left( {{- \frac{1}{2}} + \frac{1 - x}{P}} \right)L_{m}} & {L_{m} + L_{l}} & {{- \frac{1}{2}}L_{m}} & {{- \frac{1 - x}{P}}L_{m}} \\ {\left( {{- \frac{1}{2}} + \frac{1 - x}{P}} \right)L_{m}} & {{- \frac{1}{2}}L_{m}} & {L_{m} + L_{l}} & {{- \frac{1 - x}{P}}L_{m}} \\ {{{- \left( {1 - x} \right)}\gamma \; \frac{2}{P}\frac{L_{m}}{1 - \gamma}} + {{x\left( {1 - x} \right)}\frac{2}{P}\frac{L_{m}}{1 - \gamma}}} & {{- \frac{1 - x}{P}}L_{m}} & {{- \frac{1 - x}{P}}L_{m}} & {{\left( {1 - x} \right)^{2}\frac{2}{P}\frac{L_{m}}{1 - \gamma}} + {\frac{2}{P}\left( {1 - x} \right)^{2}L_{l}}} \end{bmatrix}$ wherein v_(a), v_(b), and v_(c) denote phase voltages of the motor, f denotes a closed circuit generated caused by coil turn short, P is a pole number, P/2 is a pole pair number, L_(m) and L_(l) respectively denote self inductance and leakage inductance of each phase when the motor is in a normal state, R is a phase resistance component, R_(f) is a contact resistance component generated due to inter-turn short circuit, x denotes the ratio of a faultless coil to a faulty pole, and γ is a coupling factor of pole pairs in the same as a specific phase in a slot having the specific phase.
 5. The system of claim 4, wherein fault current i_(f) due to turn short circuit is $\mspace{79mu} \begin{matrix} {i_{f} = {{\frac{{{R_{i\; 44}\left( {{\omega \; {I_{q}\left( {\text{?} - \text{?}} \right)}} - {\text{?}I_{d}}} \right)}\omega} - {\text{?}\left( {{\text{?}\omega \; I_{q}} + {\omega^{2}{\psi \left( {1 - x} \right)}\frac{2}{P}} + {\omega^{2}{I_{d}\left( {\text{?} - \text{?}} \right)}}} \right)\omega}}{\text{?} + \left( {\text{?}\omega} \right)^{2}}\cos \; \omega \; t} +}} \\ {{\frac{{\text{?}\left( {{\text{?}\omega \; I_{q}} + {\omega^{2}{\psi_{m}\left( {1 - x} \right)}\frac{2}{P}} + {\omega^{2}{I_{d}\left( {\text{?} - \text{?}} \right)}}} \right)} + {\text{?}\left( {{\omega \; {I_{q}\left( {\text{?} - \text{?}} \right)}} - {\text{?}I_{d}}} \right)\omega^{2}}}{\text{?} + \left( {\text{?}\omega} \right)^{2}}\sin \; \omega \; {t.}}} \end{matrix}$ ?indicates text missing or illegible when filed
 6. The system of claim 5, wherein a synchronous reference frame value of a voltage value obtained by filtering the output of the negative sequence current controller is as follows. $\mspace{20mu} {\begin{bmatrix} \text{?} \\ \text{?} \end{bmatrix} = {{{\frac{1}{3}\begin{bmatrix} {{I_{d}\left( {\text{?} + {2\; \text{?}}} \right)} + {\text{?}\; k_{1}} + {\omega \; {I_{q}\left( {{- \text{?}} + {2\; \text{?}} - {2\text{?}} + \text{?}} \right)}} + {\omega \; {k_{2}\left( {\text{?} - \text{?}} \right)}}} \\ {{I_{q}\left( {\text{?} + {2\text{?}}} \right)} - {\text{?}k_{2}} - {\omega \; {I_{d}\left( {{- \text{?}} - {2\text{?}} + \text{?} + {2\; \text{?}}} \right)}} + {\omega \; {\psi_{m}\left( {3 - {\frac{2}{P}\left( {1 - x} \right)}} \right)}} + {\omega \; {k_{1}\left( {\text{?} - \text{?}} \right)}}} \end{bmatrix}}\mspace{20mu}\begin{bmatrix} \text{?} \\ \text{?} \end{bmatrix}} = {\frac{1}{3}\begin{bmatrix} {{I_{d}\left( {\text{?} - \; \text{?}} \right)} + {\text{?}\; k_{1}} + {\omega \; {I_{q}\left( {{- \text{?}} + {2\; \text{?}} + \text{?} - {2L\text{?}}} \right)}} + {\omega \; {k_{2}\left( {\text{?} - \text{?}} \right)}}} \\ {{- {I_{q}\left( {\text{?} + {2\text{?}}} \right)}} + {\text{?}k_{2}} + {\omega \; {\psi_{m}\left( {\frac{2}{P}\left( {1 - x} \right)} \right)}} + {\omega \; {I_{d}\left( {{- \text{?}} + {2\; \text{?}} + \text{?} - {2\; \text{?}}} \right)}} - {\omega \; {k_{2}\left( {\text{?} - \text{?}} \right)}}} \end{bmatrix}}}}$ ?indicates text missing or illegible when filed
 7. A method for detecting a fault of a serial coil type permanent magnet motor, the method comprising the steps of: driving the serial coil type permanent motor based on a predefined current reference value; detecting a phase current vector of the motor; calculating a current compensation value for removing a negative sequence component of the motor based on the phase current vector; providing the current compensation value to a negative sequence current controller and calculating a faulty phase and a degree of a fault of the serial coil type permanent motor using the output of the negative sequence current controller and a fault model to which induced magnetic flux variations in a specific slot of a specific faulty phase of the serial coil type permanent motor and other slots of the same phase as the specific phase are applied; and applying a current reference value to which the calculated faulty phase and degree of fault are applied.
 8. The method of claim 7, wherein the step of applying the current reference value includes adjusting the velocity and phase current of the motor based on the faulty phase and degree of fault to suppress generation of overcurrent. 